Useful starting points for Algonquin Provincial Park:

Algonquin Outfitters are just outside the park. Best selection of paddles I've seen yet, if you're looking to buy. A good selection of fairly high-end equipment and the usual outfitting stuff, as well.

The Portage Store, besides being an outfitter, has a Ministry office where you can get your permit, and is right on two access points for beginning and ending your trip. There's also a restaurant (standard food, great homefries, beer) where, through big windows, you can watch people have voyages of personal discovery involving canoes.

Canoe Routes of Algonquin Park map, based on the 1994 version. PDF format, 5.5Mb. Don't try to use this unless you've got a P133 or faster, or it'll be an exercise in frustration trying to see anything.